Planographic printing plate



y 1944. w. B. WESCOTT 2,348,943

PLANOGRAPHIC PRINTING PLATE Filed April 28, 1943 Patented May 16,1944

PLANOGRAPHIC PRINTING PLATE William B. Wescott, Dover, Masa, assignor toAddressograph-Multigraph Corporation, Wilmlngton, Del., a corporation ofDelaware Application April 28, 1943, Serial No. 484,833

9 Claims.

This invention relates to planographic printing and more particularly toa parchmentized cellulose planographic printing plate, and thisapplication is a continuation-in-part of my copending application SerialNo. 471,673, filed J anuary 8, 1943. My prior patents, Nos. 2,134,165and 2,205,998 may be referred to'as showing the state of this art.

Parchmentized cellulose planographic printing plates offer numerousadvantages over the older planographic' printing plates of metal byreason of their flexibility and ease of handling in a typewriter,rendering them particularly adapted to ofice use in connection withcylinder oflset reproducing machines. However, the use of parchmentizedcellulose printing plates, though extensive, has been limited in certainrespects. Their use could have been greatly enlarged were it not for twoconditions that have not heretofore been overcome, namely, (1) the veryshort useful life of unbacked parchmentized cellulose printing plates,and (2) the difliculties, expense, and complications encountered inmaking and handling the prior parchmentized cellulose'printing plateshaving backing layers.

The very short useful life of unbacked parchmentized cellulose printingplates arises from the fact that they must absorb water as they are usedin planographic printing, and that as they absorb water they expandrapidly, principally in width. After a very few impressions suchunbacked parchmentized cellulose plates show considerable distortion ofthe image and loss of sharpness of the image, rendering them unfit forfurther use.

Backed plates consisting of parchmentized cellulose, a backing layer,and an intermediate bonding layer of water-impermeable adhesive, preventlateral expansion of the printing surface but are subject to a number ofdifficulties. Provision of a non-extensible backing for theparchmentized cellulose printing layer prevents the undesired lateralexpansion, but this expedient introduces a number of dliilculties.

Operation of the parchmentized cellulose as a planographic printingelement depends upon than water-receptive, and on the surface of theplate would behave as a grease-receptive contaminant. Parchmentizedcellulose is to some extent permeable to the adhesive. A high degree ofpressure is necessary in order to obtain the requisite degree ofadhesion between the parchmentized cellulose and the backing layer. Thispressure tends to force the adhesive both through the backing layer andthrough the parchmentized cellulose. This eflfect is heightened by thenecessary presence of plasticizers in the adhesive, the suitableplasticizers also acting as contaminants of the printing surface.Because of tiny pinholes which characterize thin parchmentized celluloseand provide paths through which the adhesive can flow toward theprinting surface, it is found impractical to use parchmentized cellulosesheets of less than 50 pounds ream weight i 24 x 36-500 basis) for theprinting surface in backed parchmentized cellulose plates.

In order to minimize the migration of the contaminating adhesive to theface of the printin'g surface it is customary to use a greater thicknessor weight of parchmentized cellulose than is needed as a printingelement. Fifty to sixty pounds ream weight has been found to be theminimum satisfactory weight, whereas if it were not for thecontamination by the adhesive its printing surface being water-receptiveat all places excepting where grease-receptive imageforming material hasbeen applied to make its image area non-receptive to water. To retainthe backing firmly adherent to the parchmentized cellulose when thelatter is moist requires an adhesive which is relativelywater-impermeable. All such water-impermeable adhesives are necessarilypreferentially grease-receptive rather of sheets of that weight,twenty-five to thirty pounds would be satisfactory.

Contamination of the printing surface may also occur as a result ofpressure contact of the printing face of one sheet with the backing ofanother,

and the complete avoidance of such contamination requires special stepsin manufacture and handling as more fully described in my copendlngapplication Serial No. 312,390, filed January 4, 1940.

Objects of the present invention are to avoid the above difficulties anddisadvantages, to provide a parchmentized cellulose printing elementthat is cheaper than the previous backed elements, and with which it iseasy to avoid contamination in manufacture and handling. These andfurther advantages are attained by the 'present invention which will nowbe described.

The invention involves the discovery that by taking twosheets ofcellulose water leaf, each in the process of being acted on by the acidin parchmentizing, at least one being adapted to serve as a planographicprinting surface upon washing and drying, and then in a manner known inthe making of laminated parchment, A laminating and cohering thesetogether while under the influence of the acid and washing the acidtherefrom, and drying, there can be made,

a sheet which is admirably suitedfizo be cut into planographic printingplates. There is no tendency, either originally or later, for theprinting surface of the plate to be contaminated by adhesive, since theJunction between the two sheets is formed of the same material as theprinting surface and is free of extraneous bonding agents. The platesare much cheaper in cost than previous backed printing plates. Theinvolved step of applying an adhesively secured backing is avoided. Thematerial requires less handling in its manufacture. No specialrequirements exist as to packing the plates. Yet compared to plates ofequal weight and equal surfaceparchmentization but composed of a singlethickness of parchmentized cellulose, the new plates take four to tentimes as long to expand a given amount in width in use on an. offsetplanographic press and hence will make four to ten times as many goodimpressions in printing.

In the drawing,

Fig. 1 is a perspective view of a printing plate made in accordance withthe present invention;

Fig. 2 is an enlarged fragmentary edge view of the printing-plate ofFig. 1; and

Fig. 3 is a schematic view indicating the principal steps inmanufacturing the material of the printing plates of the presentinvention.

Referring to Fig. 2, the material of the printing plate consistsentirely of cellulose, consisting in part of the fibrous form ofcellulose and in part of the amyloid non-fibrous form of cellulousresulting from the parchmentizing process. Among the knowncharacteristics of parchmentized cellulose suitable for use as aplanographic printing plate are: that it readily receives and retainsthe ink-receptive image-forming material (of which numerous examples areknown to ducing the material for this planographic printing plate is asfollows: a

Two webs 20 and 2! of unsized paper or waterleaf made from bleachedsulphite stock. free from any of the undesirable added components orcontaminants as explained above, are simultaneously subjected to aconventional parchmentizing treatment in a sulphuric acid bath 2!. Uponemerging from the bath and while their surfaces are still in thegelatinous state induced by the acid and still wet thereby, the two websII and II are led into contact face to face and passed between a pair ofpress rolls 2! and 2| which subiect thewebs to a pressure sufllcient toeffect a lose.

firm fusion of the contacting coherlng gelatinous surfaces of the webs.The acid and water are re-- moved by passing the composite web throughany suitable washing apparatus 21 and drying apparatus 28.

The unified sheet thus produced is then cut up into printing plateswhich are provided with any desired structure at their ends forattaching them to the printing machine. As shown by way of example inFig. 1, front and rear edges ll of inal webs. is substantially free ofany fibrous the art and further examples are set forth in my copendingapplication Serial No. 312,391, filed January 4, 1940); that it isreadily wet by and absorptive of water; and that it is free from anyadded component or contaminant which either causes the printing ink todisplace water previously applied or causes water later applied todisplace the ink-receptive image-forming material which has beeninitially applied to the dry sheet. The sheet is relatively strong andis highly resistant to disintegration by water.

As shown in Fig. 2 both the outer printing face II and thecorrespondingrear face l2 are each constituted of non-fibrous amyloidcellulose overlaying the cellulose fibers. Inwardly of the printing faceII and inwardly of the rear face l2, the non-fibrous amyloid cellulose,represented by the stippling in Fig. 2, becomes less ,dense} thereforming a net-work which is integral with the amyloid cellulose on thesurface and is bonded to the cellulose fibers with which it isintermingled. Finally, in a stratum extending through the middle of thethickness of the sheet the net-works of amyloid cellulose of the upperand lower halves are integrally joined by a dense stratum it of the sameamyloid cellulose, free from fiber. The whole plate thus consists ofunifled cellulose, contains fibers in its two halves and has extendingthroughout the plate a continuum of non-fibrous amyloid cellulose whichoverlays the fibers near each face of the plate and also forms afiber-free and dense stratum at its Junction between the two constituentsheets.

An example of the preferred procedure in pro- 76 form of cellulose.Nevertheless this middle stratum is thoroughly bonded to all of theremainder of the plate by the extension outwardly from this middlestrata of less dense but unitary amyloid cellulose bonded to theindividual fibers remaining from the two original webs.

As shown in Fig. 2, the thickness of the middle stratum I! of fiber-freecellulose is greater than the sum of the two thicknesses of thefiber-free cellulose which overlay the fibers near the two faces [I andI2. As the composite web ill, II is but surprisingly the increase indimension due to absorption of water takes place, in its initial stages,at a much slower rate (one-fourth to onetenth) than in the case of aplate of equal weight and surface-parchmentization consisting of asingle layer of parchmentized cellulose. Accordingly, within thelimitation of the desired good quality of the impressions, four to tentimes as many good impressions can be made.

The plate constitutes a valuable improvement over previous backed platesof parchmentized cellulose. There is no tendency of the absorbed waterto weaken the bond between the front and back of the sheet. All tendencytoward contamination of the printing surface by adhesive bondprintingsurface.

nous state. All difficulties with contamination of the printing surfaceby plasticizers are avoided.

It is no longer necessary to increase the thicknessof parchmentizedcellulose for the printing element for the purpose of guarding againstmigration of adhesive and its plasticiz'er to the Thinner sheets mayaccordingly be used without any resulting contamination. For instance,the two webs and 2| whichare bonded together to form the material of theplate each may advantageously have a ream weight (24 x 36500 basis) ofas low as pounds. I

-The back of the plate cannot exert any contaminating effect of the faceof another plate with which it may contact for as indicated above, noadded adhesive is applied and hence none is present to permeate the backof the sheet.

An advantage of the present invention is that the aggregate hardness ofthe printing plate is substantially greater than the aggregate hard- 1ness of a plate of equal total thickness consisting of a front layer ofparchmentlzed cellulose, an intermediate bonding layer, and a backinglayer of kraft paper, the hardness of the parchmentized cellulose beingsubstantially greater than that of' kraft backing paper. This increasedaggregate hardness of the plate results in a crisper image, particularlyin typewriting upon the plate.

It is recommended that the two component faces of the platebe'approximately balanced as to density, that is, contributesubstantially equally to the total density of the plate, in order thatthe plate may have as little tendency to curl as possible.

The expression density is herein used in reference to the compactness ofthe parchmentized cellulose.- Density of parchmentized cellulose varieswith,.and may be satisfactorily expressed in terms of, translucency oropacity, bearing in mind the fact that the opacity of a sheet of givendensity varies with the thickness so that numerical values of opacityreflect comparative densities only for sheets of the same thickness.

Within the limits of surface smoothness which are recommended, andprovided the plate is of substantially uniform opacity throughout itsarea, the opacity of the parchmentized cellulose printing plate of thisinvention is a satisfactory criterion of density of the plate as awhole. A parchmentized celluloseprinting plate of the present inventionhaving a surface smoothness of from four to eight as determined by theBekk smoothness tester and of pound ream weight and about 0.004inch inthickness should in order to have the proper density, have an opacity,as determined by the Bausch & Lomb opacimeter, of not over 0.60; theopacity of this same plate should also preferably be not less than 0.45because lower opacities than 0.45, at this thickness, indicate such ahigh degree of parchmentization as results in too great brittleness forconvenient handling. Plates of other thicknesses should'have the densityof the p ate just described, the values of opacity corresponding to suchdensity and the plate thickness.

The outer printing face II should, for typewriting and crayon work, havea smoothness of two or upwards, as determined by the Bekk smoothnesstester? while for penmanship, whether writing or line drawing, thesmoothness should be four or more. Although satisfactory results can beobtained at values corresponding toglossy surfaces, a smoothness in theoptimum range of from four to eight is preferred.

In order to absorb the dampening solution in planographic printing theparchmentized cellose of the outer printing face ll necessarily has apositive absorption for water. But an advantageous improvement in lifeof the image under printing conditions occurs if, as is preferred, theouter printing face has a rate of lateral water diffusion of not morethan 25 millimeters in four hours, while having the characteristics ,ofdensity and smoothness as above described. The lateral water diffusionrate herein referred to means the result of a test (as later hereindescribed) of the sheet in its normal condition of'inherent density, andnot while in a temporarily altered condition of density which wouldresult, for example, from calendaring the sheetafter formation, it beingwell known that calendaring may give the sheet increased density,decreased porosity, and a changed diffusion rate, all of whichcharacteristics may be restored to normal by soaking and drying thesheet.

For the present purpose the lateral diffusion rate of water in unifiedcellulosic material is defined as the height (expressed in millimeters)to which distilled water rises in a sheet of said material over a periodof 4 hours when the edges thereof are sealed against absorption of waterin any convenient manner and when the sheet is suspended over aquiescent bath of said water at room temperature under the followingfurther conditions: (1) the lower end of the sheet is maintained belowthe level of the bath, this being conveniently accomplished by folding abit of sheeted block tin over the bottom edge; (2)

the machine direction of the sheet is to be parof which time the risefrom the marker is measured off in millimeters.

A preferred way of causing the parchmentized cellulose to have thedesired low rate of lateral water diffusion, without loss of thedesirable characteristics as to density and smoothness, consists in anaccelerated oxidation of the surface of the material of the plate.

The increment in oxidation-products content due to such acceleratedoxidation may be employed as a useful measure of the. effectiveness ofthe accelerated oxidation. (By oxidationproducts content is here meantthe sum of the copper number and percentage cold alkali solubility.) Itis recommended that the accelerated oxidation be carried on to suchextent that the increment in oxidation-products content due to suchaccelerated oxidation will be atleast 10% over that of the material ofthe plate as freshly made. Improvement in press performance may beexpected to result from still greater increase 4 assaass in oxidationproducts content due to accelerated oxidation, but the acceleratedoxidation should not be carried so far as to-cause marked discolorationor embrittlement.

Accelerated oxidation of the surface of the material of the plate may bebrought about in a number of ways in which the surface of the plate isaccessible to air, oxygen or ozone. For example, exposure to sunlight iseffective but is not recommended as a commercial procedure. Exposure toartificially produced ultra violet light is effective. Ultra violetirradiation at 10 inches from a quartz mercury vapor arc lamp for from 2to 15 minutes, depending upon the reactivity of the stock being treated,will suffice. Other application of non-gaseous oxidizing agents thereto,have been tried and found to yield more or less satisfactory results.

A suitable method of predisposing the surface to accelerated oxidationby contacting the surface with anhydrous chlorine gas is disclosed in mysaid copending application Serial No. 312,390, which may be referred tofor details of such step. Following such predisposition to acceleratedoxidation the desired increase in oxidation-products content will takeplace upon mere exposure of the surface to air for a time of the orderof 1 to 3 weeks.

I have discovered that resinous extractives contained as inevitableimpurities in commercially available wood pulp tend to be the cause ofink-retentive spots which develop autogeneously on the surface of theplate. To minimize such effect, it is desirable to take two precautions.Firstly, the materialfrom which the outer printing face is made ispreferably initially selected from material which does not contain morethan 0.5% of resinous extractives. Although some a preciable quantity ofresinous extractives will be ound in all commercial grades ofpapermaking wood pulp availablefor manufacture of the plates, thisrequirement of an upper limit of 0.5% of resinous extractives can be metby the better grades of the paper-making wood 'pulp which iscommercially available. Although a certain amount of resinousextractives is inevitable, and such resinous extractives exist as' tinyparticles within the material of the plate, the parchmentizing processhas the effect of preventing any substantial number of these particlesfrom. initially being located at the printing surface of the plate.Apparently during the parchmentization the cellulose gel at and near thesurface flows over and forms a continuum covering substantially all ofthe particles of resinous extractives which might otherwise be exposedat the surface of the plate.

But the cellulose of the printing plate is permeable to resinousmaterial in the normal mobile condition of the resinous material. Tracesof such mobile resinous material initially contained in the body of theplate tend to migrate through the non-fibrous surface continuum andfinally appear on the printing surface of the plate. Even such traces ofresinous material. when exposed on thesurface of the plate, becomeinkreceptive and ink-retentive.

Therefore, as a second precaution, it is preferable to immobilize thetraces of resinous extractives contained in the printing face of thematerial of the plate and thereby prevent them from migrating to theprinting surface. The resinous extractives may be thus immobilized bysufllciently aging'either 5 plate from tendency to form ink-retentivespots due to resinous material at its printing surface may beascertained by an. accelerated test of the printing plate comprisingincubating the plate for 4 days at 150 F., irradiating the printing faceby ultra violet light from a quartz mercury vapor are lamp (Hanoviatype) for '15 minutes at a mean distance of 10 inches, thoroughlysaturating the printing surface with the etching solution described inmy United States. Patent No. 2,003,268, dated May 28, 1935, com-- knownways of oxidizing cellulose, including the prising ammonium dihydrogenphosphate, nickel or cobalt nitrate, glycerin and water, removing anysuperficial etch with blotting paper or the like, and then immediatelyrolling up a portion 2 of the so-dampened surface with a usual stiffoffset lithographic printing ink. As a result of this test, themacroscopically discernible pinpoint ink-retentive spots should not' onthe average be more than 0.5 millimeter in diameter andnot of greateroccurrence than one such spot for each has the preferred characteristicsas to surface smoothness, low lateral water diffusion rate, low contentof resinous extractives and substantial immobility of the resinousextractives', and is thus to be the only face intended for printing.

then it is desirable to differentiate the two. faces by giving one orthe other a trace of coloring so that the face intended as the printingface will be instantly apparent.

I claim:

40 l. A parchmentized cellulose planographic printing plate, theprinting surface thereof having planographic printing characteristics,and the plate being formed of two superposed sheets of parchmentizedcellulose, a continuum of nona fibrous amyloid cellulose extendingthroughoutv both sheets, said continuum overlaying the fibers near eachface of the plate and also constituting a fiber-free and dense stratumat' the Junction between the two sheets, said Junction stratumintegrally uniting the two constituent sheets,

and being free of extraneous bonding agents,

the plate having a density such as corresponds in a plate of pound reamweight and 0.004 inch thickness to an opacity of from 0.45 to 0.60,

55 the sheet material which forms the printing surface being readily wetby and absorptive of water applied to the printing surface, so as torepel printing ink in the non-imaged areas under printing conditions,but the printing surface having a lateral water difiusion rate of notmore than 25 millimeters in four hours.

2. A parchmentized cellulose planographic printing plate, the printingsurface thereof having planographic printing characteristics, and

u thezplate consisting of two superposed sheets of parchmentizedcellulose, a continuum of nonfibrous amyloid cellulose extendingthroughout e both sheets, said continuum overlaying the fibers near eachface of the plate and also constituting a fiber-free and dense stratumat the junc-' sheet which forms the printing surface portionthe woodpulp from which the waterleaf ismade, II of the plate being of woodorigin containing traces of resinous material, and said resinousmaterial being in an immobile state to prevent it from migrating to theprinting face and there causing autogenous ink-receptive spotting.

3. A parchmentized cellulose planographic printing plate, the printingsurface thereof having planographic printing characteristics, and theplate being formed of two superposed sheets of parchmentized cellulose,a continuum of nonfibrous amyloid cellulose extending throughout bothsheets, said bontinuum overlaying the fibers near each face of the plateand also constituting a fiber-free and dense stratum at the junctionbetween the two sheets, said junction stratum integrally uniting the twoconstituent sheets and being free of extraneous bonding agents, theplate having a density such as corresponds in a plate of 60 pound reamweight and 0.004 inch thickness to an opacity of from 0.45 to 0.60.

4. A parchmentized cellulose planographic printing plate, theprintingsurface thereof hav-.

ing planographic printing characteristics, and the plate being formed oftwo superposed sheets of parchmentized cellulose, a continuum ofnonflbrous amyloid cellulose extending throughout both sheets, saidcontinuum overlaying the fibers near each face of the plate and alsoconstituting a fiber-free and dense'stratum at the junction between thetwo sheets, said junction stratum integrally uniting the two constituentsheets and being free of extraneous bonding agents, the sheet materialwhich forms the printing surface being readily wet by and absorptive ofwater applied to the. printing surface, so as to repel printing ink inthe non-imaged areas under printing conditions, but the lateral waterdiffusion rate of the printing surface being not more than 25millimeters in four hours.

5. A parchmentized cellulose planographic printing-plate, the printingsurface thereof having planographic printing characteristics, and theplate consisting of two superposed fibrous sheets of parchmentizedcellulose, a continuum of non-fibrous amyloid cellulose extendingthroughout the plate, said continuum overlaying the fibers near eachface of the plate and also constituting a fiber-free and dense bondingstratum at the junction between the two sheets, said bonding stratumintegrally uniting the two constituent sheets and being free ofextraneous bonding agents, and an ink-receptive image on said printingsurface and adapted to be retained by said surface when water issubsequently applied thereto in use of the plate.

6 A parchmentized cellulose planographic printing plate, the printingsurface thereof having planographic printing characteristics, and theplate consisting of two superposed fibrous sheets of parchmentizedcellulose, a continuum of non-fibrous amyloid, cellulose extendingthroughout the plate, said continuum overlaying the fibers near eachface of th plate and also constituting a fiber-free and'dense bondingstratum at the Junction between the two sheets; said the plate.

bonding stratum integrally uniting the two constituent sheets and beingfree of extraneous bonding agents, the plate having a thickness ofapproximately 0.004 inch, and an ink-receptive image on said printingsurface and adapted to be retained by said surface when water issubsequently applied thereto in use of the plate.

7. A parchmentized cellulose planographic printing plate, the printingsurface thereof having planographic printing characteristics, and theplate being formed of two superposed sheets of parchmentized cellulose,a continuum of nonfibrous amyloid cellulose extending throughout bothsheets, said continuum overlaying the fibers near each face of the plateand also constituting a fiber-free and dense stratum at the junctionbetween the two sheets, said junction stratum integrally uniting the twoconstituent sheets and being free of extraneous bonding agents, theplate having a density such as corresponds in a plate of 60 pound reamweight and'0.004 inch thickness to an opacity of from 0.45 to 0.60, andan ink-receptive image on said printing surface and adapted to beretained by said surface when water is subsequently applied thereto inuse of the plate.

8. A parchmentized cellulose planographic printing plate, the printingsurface thereof having planographic printing characteristics, and theplate consisting of two superposed fibrous sheets of parchmentizedcellulose, a continuum of non-fibrous amyloid cellulose extendingthroughout the plate, said continuum overlaying the fibers near eachface of the plate and also constituting a fiber-free and dense bondingstratum at the junction between the two sheets, said bonding stratumintegrally uniting the two constituent sheets and being free ofextraneous bonding agents, the density of the two constituent sheets ofthe plate being substantially the same, and an ink-receptive image onsaid printing surface and adapted to be retained by said surface whenthe water is' subsequently applied thereto in use of the plate.

9. A parchmentized cellulose planographic printing plate, the printingsurface thereof having planographic printing characteristics, and theplate consisting of two superposed fibrous sheets of parchmentizedcellulose, a continuum WILLIAM B. WESCOTT.

